1. Field of the Invention
This invention generally relates to a linear motion rolling contact guide unit, and, in particular, to a finite linear motion rolling contact guide unit including a retainer for retaining a plurality of rolling members interposed between a rail and a slider.
2. Description of the Prior Art
A linear motion rolling contact guide unit is well known in the art and it generally includes a rail or base, a slider slidably mounted on the rail and a plurality of rolling members interposed between the rail and the slider. There are basically two types of such guide units. That is, one type of such guide units is of the endless linear motion type in which the slider may move along the rail as long as the rail exits; whereas, the other type is of the finite linear motion type in which the slider may move relative to and along the rail over a limited distance. In the case of the finite linear motion type, use is typically made of a retainer for retaining the rolling members in position between the rail and the slider.
One typical prior art finite linear motion guide unit is schematically shown in perspective view in FIG. 18. As shown, the illustrated finite linear motion guide unit includes a rail 22, which is elongated in shape and extends over a desired distance, and a slider or table 21 which is substantially equal in length in the longitudinal direction to the rail 22. The rail 22 is generally rectangular in shape in the illustrated structure and provided with a pair of left and right inner guide grooves 28 on its opposite side surfaces. The slider 21 is generally U-shaped in cross section and slidably mounted on the rail 22 in a straddling manner. The slider 21 is provided with a pair of left and right outer guide grooves 27 each located spaced apart from and facing opposite to a corresponding one of the pair of inner guide grooves 28. Thus, a guide channel is defined between each associated pair of inner and outer guide grooves 28 and 27, and a plurality of rolling members or rollers 23 in the illustrated example are provided in the guide channel. As a result, the rollers 23 are partly received in both of the associated inner and outer guide grooves 28 and 27 so that a rolling contact is provided between the rail 22 and the slider 21. In the illustrated example, the rollers 23 are arranged in the so-called crossed arrangement in which any two adjacent rollers 23 are arranged with their rotating axes directed perpendicular to each other when viewed into the direction of advancement.
As shown in FIG. 18, also provided is a retainer 24 in the form of an elongated plate for retaining the rollers 23 in position in the guide channel. In this structure, because of the provision of the retainer plate 24, the rollers 23 can be maintained at desired positions even if a relative motion is produced between the rail 22 and the slider 21 so that a uniform distribution of load may be maintained. However, in this structure, especially when a linear reciprocating motion is repeatedly produced, there is a chance that the retainer 24 deviates from its intended position. In particular, as shown in FIG. 19, the end surface of the retainer plate 24 may come into abutment against the tip end portion 30 of an end stopper plate 26 mounted on the rail 22 or against the tip end portion of an end screw 25 threaded into the table 21.
In such a case, since the area of abutment or contact between the end surface of the retainer plate 24 and the tip end portion 30 or 31 of either of the end stopper plate 26 or the end screw 25, when the end surface of retainer plate 24 has come into abutment against the end stopper plate 26, the retainer plate 24 tends to be deflected toward the slider 21 or to the right in FIG. 19, on the other hand, when the end surface of retainer plate 24 has come into abutment against the end screw 25, then the retainer plate 24 tends to be deflected toward the rail 22 or to the left in FIG. 19. As a result, there is a chance that the end portion of retainer plate 24 slips through the gap between the end stopper plate 26 and the end screw 25 and thus is projected out of the linear motion guide unit in an excessive instance.